1. Field of the Invention
The invention relates to an improved apparatus for preventing self-injurious behavior in patients. The invention uses a near field magnetic link to transmit a coded signal from a sensor module or from a remote actuator to a stimulus module worn on the patient. The stimulus module uses a unique flyback circuit design to generate an electrical stimulus which is tuned to achieve a maximum physiologic response with minimal power drain.
2. Description of Contemporary or Prior Art
The use of aversive stimulation to prevent certain types of behavior is known in the art. U.S. Pat. No. 3,998,209, issued to Gilbert Macvaugh on Dec. 21, 1976, teaches the application of electric shock pulses for conditioning snoring. U.S. Pat. No. 3,885,576, issued to Elliott Symmes, on May 26, 1975, teaches the use of electric shock as a means to deter smoking. In that patent a mercury switch is mounted on a wrist band so that when the user moves his arm (e.g., to place a cigarette in his lips), the mercury switch closes and allows an electric current to flow to electrodes on the user's wrist band.
The use of aversive stimulation to inhibit self-injurious behavior was first described by Mooza Grant in U.S. Pat. No. 3,834,379, issued Sept. 10, 1974. Mooza Grant describes an apparatus which conditions self-destructive patients against self-injurious blows to the head. The apparatus contains a helmet which is mounted on the patient's head to absorb self-injurious blows. The helmet contains a metallic cylinder and a movable pin disposed centrally therein. When a patient strikes the helmet, the pin contacts with the cylinder and establishes an electrical contact which activates an electronic package (described as being disposed within a jacket in patients clothes). An electric pulse generated in the electronic package is sent to the electrodes contained in an arm band and provides an aversive electric shock to the patient's arm. The helmet, electronic package, and stimulation electrodes are all connected by electrical wires.
The use of a wireless communication link between a sensor module and a stimulus module was first described by R. E. Fischell et al in U.S. Pat. No. 4,440,160, issued Apr. 3, 1984. The Fischell et al apparatus includes a means for setting an acceleration threshold so that an aversive blow to the head can be distinguished from acceleration due to the patient's regular activities. The Fischell et al device teaches the use of an event counter located in both the sensor and stimulus modules to record the occurrence of both a self-injurious blow and the application of aversive stimulation.